1. The Field of the Invention
The present invention relates to methods for manufacturing semiconductor devices. More particularly, the present invention relates to modifying the surface of a mold used for formation of planar surfaces during fabrication of semiconductor devices.
2. The Relevant Technology
During fabrication of semiconductor devices from silicon wafers, various processes are carried out prior to cutting the wafer into individual chips for packaging. At certain stages during fabrication of semiconductor devices, it is necessary to form planarized surfaces on the silicon wafer. Various methods have been developed to carry out the required planarization.
An efficient method of planarizing surface topography on a silicon wafer substrate during semiconductor device fabrication utilizes a photocurable polymer material that is applied to the wafer substrate. The polymer material is pressed against a flat quartz window of a mold, and radiant light energy such as ultraviolet light is directed through the quartz window to cure the polymer material, thereby forming a planar surface on the wafer substrate. The cured planarized polymer material can then be removed by a dry etch or chemical mechanical planarization (CMP) until the underlying topography is reached. By carefully choosing the method and application of polymer material removal, the underlying layer, such as an insulating layer of borophosphosilicate glass (BPSG), is removed at the same rate as the polymer material and results in a planar topography of the underlying layer.
A major drawback to the above method is adhesion of the polymer material to the surface of the quartz window when the polymer material is cured by light energy. Various mold release agents have been used in an attempt to alleviate the polymer adhesion problem on the surface of the mold. One mold release agent that has been used is octadecyl trichlorosilane (ODTS). A disadvantage of ODTS is that it must be reapplied to the mold window surface periodically, since this release agent wears off after repeated processing.
Another problem that occurs is that silicon wafers in a production line can have large particles of debris land on the surfaces thereof, such as particles of polysilicon from a broken wafer along the production line. If such debris-laden wafers are pressed against the flat quartz surface of a mold, the quartz surface can be scratched or otherwise damaged. Release agents such as ODTS offer no protection against surface damage of a quartz window by debris on a wafer. Such release agents also provide no protection against surface damage by hard material topography such as tungsten on a wafer.
Various other release agents have been used as surface modifiers. For example, perfluoroalkysilanes have been employed to prevent proteins from sticking to glass in biochemical processes. Another mold release agent that has been used is polytetrafluoroethylene (Teflon) formed on the mold surface as a planar sheet. While this mold release agent has good non-stick capabilities, it does not provide adequate protection against mold surface damage.
Accordingly, improved mold surface modifications are needed which overcome or avoid the above problems.
The present invention is directed to surface modifications of a mold contact surface used during semiconductor device fabrication. The modified mold surface provides effective non-stick characteristics and a mold surface that is resistant to abrasion or wear. The invention is particularly useful in modifying the planar surfaces of molds such as quartz molds used in forming planar surfaces on wafers during fabrication of semiconductor devices. The mold planar surface is adapted to contact a photocurable polymer material applied to a semiconductor wafer surface during a fabrication process. The mold including the planar surface thereof allows radiant electromagnetic energy such as ultraviolet light to pass therethrough to cure the polymer material placed against the planar surface of the mold.
In one aspect of the invention, a method for modifying a mold surface used during semiconductor device fabrication includes providing a mold having a planar surface as described above adapted to contact a photocurable polymer applied to a semiconductor wafer surface during a fabrication process. The mold surface is modified by forming a non-stick film on the planar surface of the mold, with the non-stick film including a release agent such as a fluoroalkylsilane compound. The non-stick film can be formed by a conventional coating process.
Alternatively, a non-stick film of a hard material such as diamond or diamond-like carbon can be formed on the mold surface, with the non-stick film providing protection against abrasion or wear on the planar surface of the mold. The non-stick film can be formed by various conventional processes such as chemical vapor deposition, plasma vapor deposition, sputtering, and the like. In addition, the non-stick film of diamond or diamond-like carbon can be fluorine-terminated, or can have a film of a fluoroalkylsilane compound formed thereover to provide further enhanced non-stick characteristics to the surface of the mold. For example, a modified mold surface can include a film comprising a protective first layer of a hard material such as diamond or diamond-like carbon deposited on the mold surface, and a non-stick second layer of a fluoroalkylsilane compound formed over the first layer.
In another aspect of the invention, a mold apparatus for use during semiconductor device fabrication is provided having a surface modified as described above such that a non-stick film of a fluoroalkylsilane compound is formed over the planar surface. Alternatively, a non-stick film of a hard material such as diamond or diamond-like carbon is formed over the planar surface of the mold. The non-stick film of diamond or diamond-like carbon can be fluorine-terminated, or can have a film of a fluoroalkylsilane compound formed thereover.
In a further aspect of the invention, a method for planarizing a semiconductor wafer device during fabrication includes providing a mold having a planar surface allowing transmission of radiant electromagnetic energy therethrough. The planar surface is modified with a non-stick film of a fluoroalkylsilane compound or a hard material such as diamond or diamond-like carbon formed thereover, as described above. The planar surface of the mold is contacted with a photocurable polymer material that has been applied to a semiconductor device wafer surface during a fabrication process. The photocurable polymer material which is planarized by pressing against the mold surface is solidified by transmitting radiant electromagnetic energy through the planar surface of the mold while the polymer material contacts the planar surface. The solidified polymer material is then released from the planar surface of the mold to allow further processing of the wafer.
The invention is particularly useful in modifying the surface of a quartz mold having a window that will transmit ultraviolet light therethrough. The mold surface modifications of the invention provide enhanced non-stick characteristics and protection against abrasion or wear on the mold surface.
These and other aspects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.